This invention relates to a boat lift having a plurality of synchronized lifting cables. The lift eliminates the use of a cable beam longitudinally beside the boat.
Boat lifts currently designed for use with medium and larger size vessels exhibit a number of shortcomings. Normally, such lifts feature a respective motor, winder and independently driven cable system mounted to support posts or pilings on each longitudinal side of the boat. As a result, these mechanisms tend to be quite expensive and complicated. Installation is usually time consuming and labor intensive. Utilizing multiple motors is particularly costly and inefficient. Moreover, it is often quite difficult to accurately synchronize the operation of the motors. The respective sides of the lift platform which supports the vessel are apt to be raised or lowered at different rates. The platform is thereby likely to tilt during operation.
At least one known four piling boat lift disclosed by Wood, U.S. Pat. No. 5,772,360, has eliminated independently operated cables and associated cable beams from respective longitudinal sides of the lift. Instead, that device employs a pair of motors and corresponding pulley assemblies mounted at the front and back ends of the boat lift. This apparatus continues to require a pair of motors, which are quite costly and inefficient. It also exhibits synchronization problems because of the use of multiple independent motors. Each motor in Wood operates a pair of winders having equal diameters. This requires the use of a complex differential gearing system in order to drive the winders and their respective cables at different speeds.
Most conventional multiple cable/multiple piling boat lifts experience significant problems associated with speed reduction. The output of each motor must be reduced to provide an appropriate winder speed and torque for raising and lowering the lift. Today, this almost always necessitates the use of a fairly complex reduction system.
Our pending U.S. application Ser. No. 09/585,116 discloses a boat lift which successfully addresses the shortcomings outlined above. We have further determined that, in certain applications, it would also be desirable to eliminate the longitudinal cable-accommodating beam used in this and other larger lifts. Such beams extend longitudinally between respective pairs of pilings or support posts located on one or both sides of the vessel being lifted. The so called xe2x80x9ccable beamxe2x80x9d requires the use of a significant amount of aluminum and adds significantly to the cost, weight and complexity of the lift apparatus. Extra time and expense are also required to install the longitudinal beam. A further disadvantage is that such beams usually cannot be used unless two spaced apart pilings or other types of support structures are mounted on one longitudinal side of the boat. The cable beam also has a tendency to obstruct the view in the vicinity of the boat lift. This can be a particular disadvantage when the boat lift is situated in an area which would otherwise provide an attractive or scenic view.
We have also determined that increasing the diameter of the standard cable winder or drum would tend to prolong cable life significantly. When wound about a more gradually curved winder with a larger circumference, the cable is subject to less winding stress.
It is a therefore an object of this invention to provide a boat lift which greatly reduces the expense, weight and complexity normally associated with multiple cable/multiple piling boat lifts.
It is a further object of this invention to provide a boat lift that automatically, reliably and accurately synchronizes raising and lowering of the lifting cables or wires on both longitudinal sides of the boat lift so that an improved, stable and level lifting and lowering operation is achieved.
It is a further object of this invention to provide a boat lift that eliminates the need to use longitudinal cable beams and which therefore significantly reduces the weight, complexity and expense of the lift.
It is a further object of this invention to provide a longitudinally beamless boat lift that does not require cable beams so that the time, expense and difficulty of lift installation are reduced considerably.
It is a further object of this invention to provide an aesthetically improved boat lift that eliminates the need for longitudinal cable beams so that the view in the vicinity of the lift is not unduly obscured or marred.
It is a further object of this invention to provide a multiple cable boat lift that operates much more reliably and efficiently than known boat lifts.
It is a further object of this invention to provide a boat lift that exhibits simplified, reliable drive reduction and lengthened cable life.
It is a further object of this invention to provide a boat lift that does not require a differential gearing mechanism or other complex reduction means to synchronize lift operation.
It is a further object of this invention to provide a single motor, multiple cable boat lift that may be installed and repaired relatively quickly and conveniently.
It is a further object of this invention to provide a boat lift that may be used effectively with various combinations of single and multiple part lifting cables.
It is a further object of this invention to provide a boat lift that employs lifting cables on both sides of the lift platform so that heavier boats can be effectively raised, but which mounts the entire drive mechanism on only one side of the vessel so that an improved, simplified and much more efficient operation is achieved.
This invention results from a realization that a highly efficient and much improved speed reduction may be achieved in a multiple cable boat lift by employing winder drums that have different diameters for driving the proximal and distal cables of the lift. This invention results from a further realization that by employing two pairs of winder drums with different sized diameters driven on a common axis by a single motor, opposing pairs of proximal and distal cables may be operated at respective speeds that synchronize the lifting operation. This also eliminates the need to drive at least some of the cables longitudinally relative to the lift and obviates the use of longitudinal cable beams. As used herein, a xe2x80x9cmultiple cablexe2x80x9d boat lift is intended to refer to a lift having one or more lifting cables operably attached to a lift platform on a first, proximal side of the vessel to be lifted and an equal number of distal cables for lifting and lowering the platform on the second, opposite side of the vessel.
This invention features a synchronously driven, multiple boat lift including a proximal support structure located on a first side of a boat to be lifted. There is a distal support structure located on the opposite, second side of the boat. Drive motor means are mounted on the proximal support structure for selectively operating in opposing first and second directions. A boat accommodating platform is located between the proximal and distal support structures and includes a pair of interconnected cradle beams for extending transversely beneath the boat from the first side to the second side of the boat. Each cradle beam has a proximal portion and a distal portion positionable on the first and second sides of the boat respectively. There are means operably interconnecting the motor means and the platform for synchronously raising the proximal and distal portions of the beams when the motor means are driven in the first direction and lowering the proximal and distal portions of the beams when the motor means are driven in the second direction. This enables the boat supported on the platform to be raised and lowered respectively.
In a preferred embodiment, the means for raising and lowering include a pair of proximal cables, each of which is operably connected to the proximal portion of a respective beam for enabling raising and lowering thereof and a pair of distal cables, each of which is operably connected to the distal portion of a respective beam for enabling raising and lowering thereof. The means for raising and lowering may include cable transmission means operably interconnect the motor means and each of the proximal and distal cables for retracting the cables to synchronously raise the proximal and distal portions of the beams when the motor is driven in the first direction. The transmission means advance the cables to synchronously lower the proximal and distal portions of the beams when the motor is driven in the second direction.
The means for raising and lowering preferably include a winder assembly axially rotatably interconnected to and driven by the motor means. The winder assembly may include a pair of relatively large winder drums operably connected to respective distal cables. The means for raising and lowering may also include a second pair of relatively smaller diameter winder drums operably connected to respective proximal cables. The winder drums may be mounted to the proximal support structure for coaxial rotation. It is preferred that the drums be fixedly interconnected to one another and driven by a single, common motor for rotating in unison about a common axis of rotation. In alternative embodiments, two or more motors are used, and each motor may operate one large diameter and one small diameter drum. The respective drum diameters are selected such that the proximal and distal cables are driven at a relative rate of speed that achieves synchronized raising and lowering of the sides of the lift platform. These drums may be coaxially connected.
The proximal support structure typically consists of a first support member and the distal support structure includes spaced apart second and third support members. The first support member may be located longitudinally intermediate the second and third support members. The proximal portion of each cradle beam may be located adjacent the first support member and the distal portion of each cradle beam may be located adjacent a respective one of the second and third support members. The cradle beams may thereby diverge from the proximal to distal support structures (i.e. from the first to the second sides of the vessel). Alternatively, the support structures may include a pair of spaced apart support members located on each side of the vessel. Each cradle beam may extend generally between a respective support member on the first side of the boat and an associated support member on the opposite side of the boat. Such cradle beams are preferably arranged generally parallel to one another.
This invention also features a synchronously driven, longitudinally beamless boat lift for use in combination with conventional proximal and distal support structures located on respective sides of a boat. The structure of the lift is analogous to the structure summarized above.